One thing I've always appreciated in both history and fantasy literature is the diversity of languages to be found. Yet in D&D there seems to be a dearth of languages. Well, yes, there is a substantial list of languages, but they are mostly racial or alignment tongues. As someone who prefers human-centric, Sword&Sorcery-style gaming, having Klarg the Barbarian learn "Dwarf" or "Otyugh" is next to useless, and doesn't really represent even the base-line game's assumption of humanity as the predominant race in existence.
This has always been perplexing to me, as language is not something really complicated to add to a game or implement during game play.
Historically, language was not necessarily exclusive to the scholarly realm. There's plenty of evidence that common folk around the ancient Mediterranean, for instance, where trade was common and written languages were often assumed from foreign countries, knew a few languages other than their own as a matter-of-fact, with the scholarly types being adept in a dozen or more. Even today, in geographical areas like Europe where there are a lot of languages spoken in a relatively small area, it is common to be adept at two or three languages, with a passing knowledge of several more. My friend from Hamburg speaks English and French fluently, in addition to his native tongue, and can get by conversationally in Italian, Spanish, and Portuguese, and professes to have never studied a foreign language past what passes for high school over there.
Here in America, we seem to be more exclusive than most in our "native" tongue, eschewing other languages nearly to the point of hostility, so perhaps this is the reason more diverse tongues never really worked their way into D&D or other contemporary RPGs. Or maybe I'm just more obsessed with it than Gygax, Arneson, and company were. :-)
For this entry, I'm presenting some "basic" languages to use in your games. Each language has a generic name so it can be easily dropped into any campaign; you may want to rename each, as appropriate, to give it that much more flavor.
For my campaign, I'm allowing characters to start with up to two languages, with more based on their Intelligence bonus (as many as 1 if you're using S&W, or as many as 3 with LL) with the ability to learn more languages upon gaining odd-numbered levels (3rd, 5th, etc). You may want to increase or decrease that according to your preference, or just base their learning new tongues on some in-play criteria.
"Common"- this remains the baseline language of local human culture. By that I mean the generic national language native to the majority of your PCs.
"Elder Common"- this tongue is an older version of common, perhaps comparable to Old English or Latin, out of use by common folk, but still learned and used to an extent by scholars, nobility, and perhaps the magic users in your campaign.
"Arcane"- this is the language of magic, used exclusively by those properly inducted into the secretive guilds and orders who practice the arcane arts. More a language of "science" than of conversation, not unlike what you may hear physicists rattling off;-)
"Eastern"- this is language of plain-and-steppe nomads, like the Scythians or Mongols. Useful to know for PCs frequenting oft raided borderlands, or dealing with the plentiful mercenaries from these lands. Its written form is very limited, but its militaristic focus can be useful for secret missives and the like.
"Desert"- this is the common tongue of the nomads and teeming cities of the arid desert lands. It is also useful as a scientific tongue, as many prolific engineers and architects hail from these lands, and the written form is both extensive and expressive.
"Wild"- This is the tongue of the "Old Folk". Not unlike the celtic or viking languages, it is the language of the remnants of the old tribes still practicing the old druidic ways, and often confined to the wilder corners of the civilized world. Its written form is runic, and often found carved in megalithic stones and cairns.
"Equitorial"- this is language of the jungles of the deep southern areas. There are countless varieties and dialects as one moves from tribe to tribe, but a basic understanding can be achieved. A necessary language for explorers of lost worlds and exotic locales.
"Trade"- the language of traders and merchants, serving a role similar to the tongues of Phoenicia or Venice. Always useful to know, as almost any civilized land you travel to will have at least a few individuals conversant in this language for the sake of the greatest motivator of all: gold!
"Ancient"- the language of lost civilizations. Likely found only spoken by obscure cults, lost cities, and with a written form appearing as pictographs or hieroglyphs. Another useful tongue for adventurers, at least for those with more scholarly tendencies.
"Pidgin"- the mish-mash language of pirates and dark ports of call that serve as melting pots for the thieves and rogues of dozens of cultures and races. Useful to know for adventures of a dubious nature, and the foundation for what is sometimes known as "thieves cant".
At any rate, I hope these 10 can get you started. The next step is, of course, to actually utilize them in your campaigns, the easiest ways being through treasure maps, tricky employers, and expeditions to faraway places. If you make it more profitable through gold and xp.s for your players to to be proactive in learning and utilizing the many languages of your campaign setting, they'll adopt the custom quickly, and give that much more atmosphere and immersion to your game!
I have to say my favorite "new" artist of the "old" school is one Pete Mullen. If you've not yet taken a gander at the art on his web-site, you're missing out. Seriously, this gentleman's stuff is the most inspiring, imaginative work I've seen since since EO's heyday. Its very cool to me just how thoroughly Mullen "gets it", when it comes to capturing the old-school spirit (hence my compulsion to festoon my blog with his work in every free space I can find ;). Everyone I show the Swords & Wizardry core book to has to stop and marvel at the cover. 
